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Confined Spaces

Confined spaces are a major hazard to workers who are required to work within these areas. Confined spaces include, but are not limited to, storage tanks, process vessels, pits, vats, vaults, sewage digesters, sewer silo, tunnels, manholes, utility vaults, pumping stations, enclosed grit chambers or similar types of enclosure with limited access and without proper ventilation. (See Figure 1.) Entry into confined spaces may be for the purpose of inspection, testing of equipment, maintenance (repair and cleaning) or an emergency.

To prevent confined space deaths and injuries, the Occupational Safety and Health Administration (OSHA) issued its final rules on Confined Spaces (29 CFR 1910.146) in January 1993.

Identifying a confined space

The characteristics of a confined space are:

• A space that is large enough and so configured that a worker can enter and perform assigned duties.
  
  
• A space that by design that has limited openings for entry and exit. Openings are usually small in size and difficult to move through. Small openings may make it difficult to get needed equipment in or out of spaces, especially personal protective equipment needed  or entry and work, or life- saving equipment needed for rescue.
  
  
• A space not designed for continuous employee occupancy. Most confined spaces are not designed for employees to enter and work in on a routine basis. They are usually designed to store products, enclose materials and processes, or to transport products or substances. However, workers must enter these spaces occasionally for inspection, maintenance or cleanup.

Hazards of confined spaces

Hazardous atmospheres

The most common hazard in a confined space is a hazardous atmosphere. These hazards include oxygen-deficient, oxygen-enriched, flammable or toxic atmospheres.

Oxygen

An oxygen-deficient atmosphere means that there is not enough oxygen in the space. Normal air is made up of 20.8 percent oxygen. An oxygen-deficient atmosphere has less than 19.5 percent of oxygen. Levels below 10 percent can cause unconsciousness and levels below 8 percent can quickly cause death.

Low oxygen levels in confined spaces can be caused by:

• chemical reactions;
  
  
• the breakdown of sewage or other organic matter, such as domestic waste and plant life; and
  
  
• work being done in the space, such as welding, cutting or brazing.
  
  

In order to have safe working conditions in a confined space, the oxygen level must be between 19.5 and 23.5 percent. Any level below 19.5 percent is dangerous and will affect the worker’s health and safety. If a confined space has less than 19.5 percent oxygen, it must be ventilated and should not be entered without a self-contained breathing apparatus (SCBA) approved by the National Institute of Occupational Safety and Health (NIOSH).

An oxygen-enriched atmosphere (too much oxygen) — above 23.5 percent — will cause flammable materials, such as clothing and hair to burn violently when ignited. Never use pure oxygen to ventilate a confined space. Ventilate with normal air that consists of 21 percent oxygen, 78 percent nitrogen, and 1 percent noble gases.

Flammable atmospheres, caused by the buildup of methane or other flammable dusts, gases or vapors can cause deadly fires and explosions. An explosion can only occur when a certain mixture of a fuel and air is present. If there is too little fuel, then the mixture will be too lean to burn.

If a source of ignition (e.g., sparking or electrical tools) is introduced into a confined space where the fuel mixture is above the LEL and below the UFL, then a fire or explosion may occur. Use only explosion-proof equipment and spark-proof tools in a confined space.

Other atmospheric hazards

Toxic gases and vapors come from a wide variety of sources.

Naturally Occurring

The three most common naturally occurring toxic gases found in confined spaces are carbon monoxide, hydrogen sulfide and methane. They originate inside wastewater treatment facilities/sewers by the natural breakdown of sewage, sludge or rotted material or as a result of chemicals added in the plant to treat the sewage.

• Hydrogen sulfide is a flammable, colorless gas that is created by the decay of organic matter that is found in sewers and sewage treatment plants. Hydrogen sulfide has a strong “rotten egg” odor. Workers who come in contact with hydrogen sulfide quickly lose their ability to smell the gas, even though the gas is still present.
  
  
• Carbon monoxide is a very toxic, colorless, odorless combustible gas that is a product of incomplete combustion. It is created by arc welding and combustion engines. In high concentrations, carbon monoxide can cause death by asphyxiation.
  
  
• Methane is a colorless, odorless, flammable gas. It displaces breathable air in a confined space and can cause suffocation. The most common source is the natural decay process of materials such as raw sewage, leaves or weeds.

Outside the Plant

Toxic gases and vapors can also originate from outside the wastewater treatment process. Chemical spills or illegal dumping can cause large amounts of toxic materials to enter sewers and treatment plants. Substances spilled or dumped into sewers can cause short-term or long-term health effects, as well as explosions. The dangers of toxic discharges are often complicated and unpredictable. For example, two harmless substances dumped into the sewage system miles apart can combine down-line to produce a chemical reaction that results in the release of a poisonous gas by the time it reaches the workers.

The types and quantities of toxic chemicals a worker may be exposed to depend on the industries in the surrounding area. Major categories of toxic chemicals include:

Organic Compounds

Thousands of commercially available organic substances may find their way to a plant. Contamination may be especially bad if the sewage plant receives wastes from a chemical or pesticide plant. Many of these chemicals “volatilize” or evaporate as they pass through sewers and the treatment plants (especially grit chambers, wet wells, settling tanks, aeration basins and throughout the activated sludge process). Evaporation of these substances also contributes to general air pollution. In sewers and enclosed areas, chemical fumes accumulate which may be explosive, flammable and dangerous to breathe.

The most common organic compounds dumped or spilled into sewers are:

• Gasoline from service stations is irritating to skin, eyes and mucous membranes and contains several organic compounds that can be dangerous. Most notable are hexane, which can cause nerve damage (peripheral neuropathy) after chronic exposure; and benzene, which affects the formation of blood cells and the bone marrow, and causes leukemia — a cancer of the white blood cells.
  
  
• Pesticides such as malathion, parathion, and 2,4-D are just a few of the more common chemicals that can cause nerve damage, cancer and birth defects or miscarriages.
  
  
• Cancer-causing agents such as PCBs found in electrical transformers and storage dumps often find their way into the sewage system as do solvents and degreasers such as methyl chloroform, benzene, trichloroethylene and carbon tetrachloride.
  
  

Acids and Alkalis

Acids (sulfuric, nitric and hydrochloric) and alkalis (potassium hydroxide, sodium hydroxide and ammonia) are also frequently discharged into the sewage system. Acid and alkali fumes and vapors can irritate a worker’s nose, throat and lungs.

Chemicals Used in Sewage Treatment

It is very important for workers to know the particular substances that could be found in a particular confined space that will be entered. Solvents, pipe grouts, paints, pesticides and other materials can cause serious health effects.

Other hazards of confined spaces

Entrapment

Spaces with sloping, converging walls that empty into smaller cross sections, can trap a worker in the cross section, causing suffocation or severe injury.

Falling Objects

Workers in confined spaces should be aware of the possibility of falling objects, especially in spaces that have topside openings, and where work is being done above the worker.

Unguarded Machinery

Machinery that is unguarded and may strike a worker, cause feet or hands to be caught or cause any other kind of injury can also cause hazards to employees who work in confined spaces.

Electrical Hazards

Shocks and electrocutions are all too common in wastewater treatment facilities. To control electrical hazards in the facility, routinely inspect all electrical equipment and tools, use ground fault circuit interrupters (GFCIs) or low voltage transformers.

Access with Ladders

It is essential that authorized entrants be able to safely enter and quickly evacuate the permit space. Fixed or portable ladders are commonly used for access. In many situations ladders maybe the only means of entry and egress.

• Ladders must be equipped with a non-slip base and should be tied at the top.
  
  
• Extend the ladder at least 3 feet above the top of the surface.
  
  
• The ladder should be placed so that the horizontal distance from the base to the vertical plane is approximately 1¼4 the ladder length. For example, place a 12-foot ladder so that the base is 3 feet from the wall.
  
  
• The ladder must be maintained in good condition and should be inspected prior to each use. A fixed, permanent ladder in a confined space should be checked visually for slippery or corroded rungs prior to using it.
  
  
• If a worker is at risk of falling from a ladder, have the employee wear a full body harness attached to a fall-arresting and retrieval device.
  
  

Lighting

Adequate lighting must be provided to allow authorized entrants to safely enter and exit the confined space, and to perform their work tasks. If flammable or explosive atmospheres are possible, lighting must be intrinsically safe (explosion proof). To prevent electrocutions when water may be present, lighting must be connected to ground fault circuit interrupters (GFCI).

Animals

Sewers, wastewater treatment plants and other confined spaces can contain snakes, rats and other dangerous animals. Protective equipment, exterminators or other physical changes to the workplace may be needed.

Trenching and Excavation

Sewer, water maintenance and other public works personnel may perform excavation and trenching operations in order to service broken lines or replace valves.

Workers are killed when excavated soils fall back into the excavation, when the walls of the trench or excavation collapse, or when water collecting in a trench causes the soil to become unstable. A protective system such as shoring must be installed in trenches or excavations before workers enter them.

Trenches and excavations may also contain hazardous atmospheres. For example, excavations in landfills and trenches dug around sewer lines may have a potential for containing methane, hydrogen sulfide or some other flammable or toxic gas to accumulate in the trench or excavation. There may also be a potential for an oxygen-deficient atmosphere in the trench or excavation. As mentioned above, there may also be engulfment (a common problem in unsloped, unshored excavations) or other physical hazards in the trench or excavation.

For additional information, see the AFSCME Manual on Trenching and Excavations.

Entering a confined space

All confined spaces need to be considered immediately hazardous to life until proven otherwise. When unexpected hazards arise, the escape or rescue of a worker may be difficult due to the limited number of entrances or exits. Therefore, entry into a confined space requires planning in advance to deal with potential hazards.

Permit-required/Non-permit required confined space

The employer is required to evaluate the workplace to determine if there are any potential or actual hazards in any of the confined spaces in the workplace. Based on the hazards present, these spaces will be categorized as permit-required or non-permit-required confined spaces.

A permit-required confined space has:

• potential to contain a hazardous atmosphere;
  
  
• material that can cause the engulfment of a worker;
  
  
• an internal shape that might cause a worker to be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross section; or
  
  
• contains any other recognized serious health hazards.
  
  

If there are permit-required spaces in the workplace, the employer must inform exposed workers of the existence, location and danger of the permit-required confined space by posting danger signs or by another effective method.

Non-permit-required confined space

A non-permit-required confined space is a confined space that does not contain any hazards capable of causing death or serious physical harm, and has no atmospheric hazard, nor the potential for any atmospheric hazard. These conditions must be verified by the employer.

Worker responsibilities

Entrants

The entrant is the worker who will enter the confined space to do the work. Prior to being allowed to enter a permit-required confined space, workers must receive training and be able to identify the hazards that they may face during entry. The employer is responsible for making sure that entrants use all personal protective clothing and safety equipment required for a safe entry. The entrant is responsible for self-monitoring, both by using monitoring equipment and by continually checking his or her physical conditions in the space.

Attendants

The attendant is the person stationed outside the permit-required confined space. He or she must be in constant communication with the entrant — to monitor the entrant’s status and to alert the entrants of the need to evacuate the space. For the entrant, the attendant is the only communication link to the outside of the confined space. The attendant is responsible for making sure the entrant remains safe. There are a number of things the attendant must do to protect the entrant:

• ensure that the ventilation system, if used, is operating and effectively ventilating the work area;
  
  
• monitor the atmosphere, using monitoring equipment;
  
  
• maintain constant communication with entrant;
  
  
• never leave the post unless relieved by another trained attendant;
  
  
• perform non-entry rescue;
  
  
• if used, attend the life line attached to the entrant;
  
  
• attend the air line, if used, to prevent it from getting tangled or kinked. NOTE: Air lines may only be used if accompanied by an emergency escape bottle;
  
  
• notify the entrant if the air line gets tangled or kinked or there is any other reason to evacuate the space;
  
  
• summon help if an emergency situation arises; and
  
  
• never enter the confined space unless he or she is trained to perform a rescue, and unless another attendant has arrived to relieve him or her.
  
  

Permit-required confined space entry program

A written confined space entry program must be developed and implemented if an employer has its workers enter permit-required confined spaces. The program must be available for inspection by workers and their authorized union representatives. In this program, the employer must describe how he/she will comply with the requirements of the standard. The written program must include the following:

• the procedure that the employer will use to implement the measures necessary to prevent unauthorized entry;
  
  
• identification and evaluation of the hazards of permit spaces before employees enter them;
  
  
• a list of equipment needed to perform a safe entry operation;
  
  
• procedures for atmospheric testing of the space;
  
  
• provision for at least one attendant outside the space;
  
  
• provision for responding to emergencies if attendant is monitoring more than one space;
  
  
• designation of all persons with active roles (e.g., entrants, attendants, persons who test and monitor) and provision of required training;
  
  
• procedures for summoning rescue and emergency services;
  
  
• system for the preparation, issuance, use and cancellation of entry permits;
  
  
• the system developed and implemented for closing off the permit space and cancellation of entry permits;
  
  
• procedures to coordinate operation where more than one employer (such as a contractor) is involved;
  
  
• procedures for evaluation and correction of entry operations when the employer has reason to believe that the program is not sufficiently protective; and
  
  
• the mechanism by which the confined space permit entry program is reviewed.
  
  

Entry permit

An entry permit must be filled out before a worker enters a confined space (and posted at or near the confined space). It should contain the following types of specific information concerning:

• identification of space;
  
  
• purpose of entry;
  
  
• date and duration of permit;
  
  
• list of authorized entrants;
  
  
• names of current attendants and entry supervisor;
  
  
• the hazards of the permit space to be entered;
  
  
• the measures used to isolate the permit space and eliminate or control hazards;
  
  
• the acceptable entry conditions;
  
  
• the results of atmospheric monitoring;
  
  
• rescue and emergency services that can be summoned and the means for summoning those services;
  
  
• the communication methods used by entrants and attendants to maintain contact;
  
  
• any other safety information necessary for the specific space; and/or
  
  
• any additional permits, such as for “hot work” (welding).
  
  

The entry permit is the document that certifies that the employer complies with the requirements of the standard for entries in permit-required confined spaces. Also, the entry supervisor must close off the space and cancel permits when an assignment has been completed or when prohibited conditions exist. All new conditions must be noted on the canceled permit and used in revising the permit space program. The standard also requires the employer to keep all canceled entry permits for at least 1 year.

Monitoring for atmospheric hazards

Monitoring Before Entry

Air monitoring must be conducted before entry to determine if acceptable entry conditions exist in the space. Once the initial monitoring is completed, the monitor may then be carried by the entrant into the confined space.

It is important to monitor at the top, middle and bottom of each permit space. Some gases, such as methane, are lighter than air and will tend to be present near the top of the space. Other gases, such as carbon monoxide, are the same density as air and will be found near the middle of the confined space. Still other gases, like hydrogen sulfide, are much heavier than air and will tend to be present near the bottom of the confined space. A good rule of thumb is to monitor every 4 feet down, if possible.

Some workplaces use more than one monitoring device to check for atmospheric hazards in confined spaces–one for each gas. If you use more than one meter in your workplace, remember you must test for these hazards in the following order:

1. Oxygen

Before entering the permit space, workers must always test for oxygen content in the air. Oxygen testing must be done before testing of flammable or explosive gases or vapors. If there is not enough oxygen in the space, the meter (monitor) will not be able to detect the presence of flammable or combustible gases. Too much oxygen in the confined space can blow the sensors in the monitoring equipment, making the device useless until the sensors have been replaced.

2. Flammable or Combustible Gases or Vapors

Workers must test for the presence of flammable or combustible gases or vapors. Entry is not allowed if a concentration greater than 10 percent of the Lower Explosive Limit (LEL) is detected. The LEL is the lowest concentration (air-fuel mixture) at which a gas or vapor can ignite. Every mixture needs a certain amount of fuel to ignite. Below this level — the LEL — there is not enough of the chemical to ignite — the mixture is too lean.

For example, methane has an LEL of 5 percent in air. That means there are five parts of methane in every 100 parts of air. At or above that concentration, a sparking tool or some other ignition source will cause the mixture to flash and burn.

The combustible gas indicator monitoring device indicates when 10 percent of the LEL has been reached. In the case of methane, this level is 0.5 parts of methane per 100 parts of air (0.5 percent is 10 percent of the LEL).

The OSHA standard thus provides a safety factor. Workers are forbidden to enter or stay in a space if any more than 10 percent of the LEL has been reached.

3. Toxic Chemicals

Workers must monitor for the presence of toxic chemicals such as carbon monoxide and hydrogen sulfide. The monitor reads these gases in parts per million (PPM). For example, the monitor may read hydrogen sulfide (H2S) at 2ppm. That means that you have a concentration of 2 parts of H2S gas per million parts of air. While that concentration is not in excess of the Permissible Exposure Limit (PEL) of 10ppm set by OSHA, it does reveal a problem in the confined space.

4. Other Hazards

If the space may contain other atmospheric hazards, such as temperature extremes (heat or cold), then these hazards must also be monitored.

If testing reveals an oxygen deficiency or an oxygen-enriched atmosphere, the presence of flammable gases or the presence of toxic gases or vapors, the space must be ventilated and retested before workers may enter. If ventilation is not possible and entry is necessary, for example in emergency rescue, workers must have appropriate respiratory protection.

Monitoring During Entry

OSHA requires that permit spaces be monitored as necessary to determine that acceptable entry conditions are being maintained. In some confined spaces that can be isolated (closed off), such as tanks or vaults, this may mean frequent monitoring or continuous monitoring, depending on the conditions.

In storm sewers, sewage collection lines, water distribution lines, vaults, lift stations or other areas which are part of a continuous system, it is not always possible to determine if acceptable entry conditions exist before entry. Hazards may exist at distances far from the entry point, and new hazards may enter the system at any time. For this reason, OSHA requires that air monitoring in continuous systems be conducted continuously — from pre-entry testing until the last entrant leaves. Continuous monitoring means that the person(s) entering the confined space must carry the monitoring device with them into the space. While the entrant is performing work in the space, the monitoring device continues to look for changes in oxygen content or the presence of flammable and/or toxic gases.

It is important to check the monitor before you enter the space to make sure that the alarm is working properly. All monitors should have an alarm that can be heard by the entrant or attendant above background noise levels. The alarm sounds if the levels of oxygen, flammable gases or toxic gases are too high or, in the case of oxygen, if the level is too low. Many monitoring devices are also equipped with a visual alarm — a light which will flash rapidly at the same time that the alarm goes off.

Monitoring Equipment

Monitoring equipment designed for use in permit-required confined spaces must be “direct reading instruments.” (See Figure 7.) These monitors draw air over a network of sensors inside the monitor. The sampled air is then analyzed inside the monitor to determine whether an atmospheric hazard exists. The results of that analysis are then directly reported to the operator of the equipment on a digital readout on newer monitors, or a needle gauge on older models.

Many monitors must be “calibrated” after every use in an environment that has similar heat and humidity conditions as the confined space. The manufacturer’s recommendations should be strictly followed. Many monitoring devices must be “zeroed” before each use by exposing the monitor to clean air and setting the indicator to zero. Just turning the instrument on is not enough. The indicator must be zeroed frequently in a clean environment when monitoring an area for an extended period of time.

Ventilation

If the atmosphere is found to lack oxygen or contain unsafe levels of toxic gases and vapors, the space must be mechanically ventilated before entry. An air-powered ventilator placed at the top of the opening can blow breathable air into the space. Ventilation must continue until safe levels exist. Just taking the top off a manhole for a period of time so that it can “air out” may not provide enough natural ventilation to make the space safe.

If the space contains an unsafe atmosphere, it may have to be mechanically ventilated. Ventilating a space before entry to clear out all contaminants is usually referred to as purging the space. Purging should take at least 10 to 15 minutes depending on the size of the confined space. The larger the space, the more time this process will require. The forced air ventilation should ventilate the immediate areas where an employee is or will be working within the space. Ventilation should be continuous where possible, because in many confined spaces the hazardous atmosphere will form again when the flow of air is stopped.

Equipment

The equipment needed to properly ventilate a confined space consists of a
blower (electrical or gas powered) and a long hose. Electrical blowers are safer than gas-powered blower and they are quieter if night work is required. A blower that has the capability to provide 600 cubic feet per minute of fresh air should be used. The hose should be 6 to 10 inches wide and long enough to reach the bottom of the confined space.

Protective equipment

Personal protective equipment is used to protect workers only after all other feasible means have been used to control or eliminate hazards. A full body or chest harness and a life line should be used when entering a confined space.

In some situations, a respirator will also be needed. Air-purifying respirators can filter dangerous substances from the air, but they provide no protection in an oxygen deficient environment and should not be used when working in a confined space. Only air-supplying respirators (SAR/SCBA) should be used in confined spaces. An air-line respirator can only be used if the worker has a rescue bottle.

Hardhats, safety goggles, face shields, gloves, safety shoes, boots, disposable suits, ear plugs or muffs, non-sparking flashlight and tools may also be needed when entering a confined space.

Rescue

An emergency in a confined space can kill an entrant in a matter of minutes. In order to facilitate rescue without having a rescuer enter a space, OSHA requires the use of “non-entry” rescue retrieval systems or methods, such as tripods and winches to lift unconscious or injured entrants out of a space that is more than 5 feet deep. In vertical entries, the safety harness should be attached to a retrieval device that will allow quick removal of an employee in the event of an emergency. In the event of an emergency, the attendant located on the outside should be able to initiate a rescue without entering the space. (See Figure 8.)

Where entry must be made for rescue, OSHA allows rescue to be performed either with the facility’s trained in-house rescuers or by contracting to an outside rescue service.

In-house Rescue: Rescuers must have extensive training. No worker — even an attendant — is authorized to enter a space to rescue an entrant unless he or she has had extensive training in personal protective and rescue equipment. This includes actual practice in making simulated rescues and CPR. NOTE: Even a trained attendant may not enter a space to make a rescue — even if he or she is trained — until another attendant has arrived.

Outside Rescue: A very controversial part of the OSHA’s Confined Space regulation is the ability of employers to use outside rescuers such as fire departments. If this is done, the rescue service must be informed of the hazards they may confront, and the rescue service must have access to all permit spaces so that the rescue service can develop appropriate rescue plans and practice rescues before a rescue must be made. NOTE: Never assume that the local fire department or rescue squad is trained or equipped to make a confined space rescue unless the requirements listed above have been met. It’s not enough to just assume you can call 911 in an emergency.

Training

Proper training, careful preparation and good judgment are essential to safe confined space entry. The employer is required to provide initial and refresher training to equip employees with the understanding, skills and knowledge necessary to perform the confined space entry safely.

Training should be provided to each affected worker before performing assigned duties in confined spaces. The entrant must be certified by the employer. Entrants, attendants, supervisors and rescuers require different levels of training according to their specific duties and responsibilities.

While OSHA does not require any specific number of hours for training, AFSCME recommends that the minimum amount of training for an entrant or attendant should be 24 hours; where there has been previous training on respirator use and air monitoring, 16 hours may be sufficient. Training for rescuers should be at least 40 hours.

For additional information, refer to Confined Spaces: An AFSCME Manual.

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